import java.util.Scanner;

public class Test1 {
    public static void main(String[] args) {
        Scanner aa = new Scanner(System.in);
        int n = aa.nextInt();
        int a = 1;
        int b = 1;
        int c = 0;
        for (int i = 2; i < n; i++) {
            c = a + b;
            a = b;
            b = c;
        }
        System.out.println(c);
    }
}